Priming a pen is not optional

The aseptic sequence is short and it is routinely compressed. Wash hands. Swab the vial stopper with alcohol and allow it to dry, because a wet stopper carries organisms into the vial on the needle. Swab the skin and allow that to dry too, both for antisepsis and because injecting through wet alcohol stings and is what people mistakenly attribute to the drug. Use a new needle. None of this is demanding, and all of it is what stands between a multi-dose vial and a contaminated one.

What the diluent changes, and what it does not

The diluent has no effect on the arithmetic and a substantial effect on everything else. Bacteriostatic water contains a preservative, conventionally benzyl alcohol at around nine tenths of a per cent, which inhibits microbial growth and is what makes repeated puncture of a multi-dose vial defensible. Sterile water for injection contains no preservative and offers no protection after the first puncture. Sodium chloride solution is isotonic and generally more comfortable on injection, and preserved and unpreserved presentations both exist.

The choice is therefore a sterility decision rather than a convenience one. A vial that will be entered more than once and kept for weeks is a different proposition from a single-use preparation, and the presence or absence of a preservative is the difference.

Two cautions belong here. Benzyl alcohol is not appropriate in all populations and is specifically avoided in neonates. And no preservative rescues poor technique: bacteriostatic means growth-inhibiting, not sterilising, and a stopper swabbed carelessly with a needle passed through a wet surface will introduce organisms that the preservative was never intended to handle. The diluent is a margin, not a permission.

Alcohol on a stopper needs to dry to have done anything, so contact time is part of the step rather than an optional refinement. It is the detail most instruction sheets omit and the one that decides whether the wipe was worth doing.

Priming, and what skipping it costs

Pen devices require a priming step — commonly a dial to two units and an expulsion until a drop appears at the needle tip — before each injection. It serves two functions: expelling air that has accumulated in the cartridge and needle, and confirming that the device and needle are patent before a dose is dialled.

Skipping it produces an intermittent underdose. Air occupies part of the delivered volume, so some of the dialled dose is gas. Because the loss is variable and invisible, the person experiences an occasional week that felt different rather than a device error, and the habit erodes precisely because the feedback is unreliable.

Two adjacent points belong with it. A pen needle should be attached immediately before use and removed immediately after, because a needle left in place allows solution to leak out and air to be drawn in, which is how cartridges come to contain air in the first place. And the ten-second hold at the end of an injection — plunger fully depressed, needle still in the skin — exists because delivery is not instantaneous at these bore sizes, and withdrawing early leaves part of the dose on the skin. Both are omitted routinely.

Aseptic technique, in four steps

Wash hands. Swab the vial stopper with seventy per cent alcohol and let it dry. Swab the injection site and let that dry. Use a new sterile needle for every entry into the vial and every injection.

Each step has a reason that is worth knowing, because steps with unexplained reasons are the ones that get dropped. The stopper is the sterile barrier of a multi-dose vial and a needle passed through a contaminated or still-wet stopper carries organisms directly into the solution. Alcohol works by evaporation as much as by contact, so a wet surface has not been disinfected — and injecting through wet alcohol stings, which is frequently misattributed to the drug. A needle that has already pierced a rubber stopper is blunted and no longer sterile.

What none of this can do is make an unknown preparation safe. Aseptic technique protects a sterile solution from contamination during handling; it does not sterilise a solution that arrived contaminated, and it does nothing whatever about bacterial endotoxin, which is heat-stable, filter-passing and invisible to any purity assay. Research-use-only material is not manufactured, tested or released to any human sterility standard, and careful technique does not change that.

Compounds discussed here are sold for research use and are not approved for human use in any jurisdiction. The arithmetic in this department is published because incorrect arithmetic is worse than none, not as an encouragement to perform any of it.

Sharps disposal

A used needle is a biohazard to whoever encounters it next, most often a waste worker. In most jurisdictions disposal of sharps in household waste is prohibited, and in all of them it is a route by which a stranger is injured.

The mechanism is simple and free almost everywhere: a rigid, puncture-resistant sharps container, filled to the marked line and no further, returned to a community pharmacy, a local authority collection point, a needle-exchange service or a clinical waste scheme. Improvised containers — a detergent bottle, a coffee tin — are widely used and generally accepted by collection services when rigid and sealed, though a purpose-made container is inexpensive.

Needle-clipping devices exist and remove the sharp tip. They reduce but do not eliminate the hazard and do not remove the disposal obligation.

The Journal raises this for a specific reason. We have heard from readers with two or three years of accumulated sharps in a drawer, kept there because they did not know where to take them and did not want to explain what they were for. Collection services are not interested in the contents of your vials. That is a real barrier built entirely out of anticipated judgement, and it is worth naming so that it can be dismissed.

Needle reuse

Needle points are manufactured sharp, coated and single-use. A single insertion blunts and deforms the tip measurably; electron micrographs of reused needles show visible damage after one use and substantial deformation after several. Reuse is more painful, produces more tissue trauma, and is a documented risk factor for lipohypertrophy.¹

It is also extremely common, for reasons that are economic rather than ignorant. Needles cost money, they are sometimes hard to obtain without a prescription, and the harm from reuse is cumulative and invisible rather than immediate. A person reusing a needle is usually making a rational short-term decision with a poorly signposted long-term cost.

Two aggravations are worth stating. A needle left attached to a pen between doses allows leakage out and air in, which is a dosing problem as well as a sterility one. And a needle reused into a vial blunts the stopper, coring rubber fragments into the solution over repeated entries.

The Journal reports the practice without moralising about it, and notes that of all the technique failures in this file, this is the one most responsive to needles simply being cheap and available.²

Our practical conclusion is that the useful defences here are structural rather than attitudinal. Write the concentration on the vial. Recalculate at every new vial. Keep one syringe type. Change one variable at a time. Exhortations to be careful do not survive a bad week; a number written in marker on a piece of tape does.